Method for patterning magnetic films

ABSTRACT

A method of patterning magnetic devices and sensors by double etching, which includes forming a layer of dielectric on a substrate; depositing a thin adhesion layer and a thin seed layer; applying a thin resist frame to pattern a structure; cleaning the metal surface to prepare for plating; electroplating to fill up the structure and the uncovered field area, which uses a paddle cell with a permanent magnet providing magnetic field to induce magnetic orientation; stripping the resist frame; etching the seed layer/adhesion layer exposed below the resist frame down to the dielectric surface; etching the rest of magnetic materials and the seed layer using electrolytic etching in the field; etching the adhesion layer in the field, and repeating the steps for building structures with multiple levels.

TECHNICAL FIELD

This invention relates to the method of obtaining optimized magneticorientation and undercut free patterning of magnetic films by a doubleetching approach, and particularly to a method of patterning magneticdevices and sensors by double etching.

BACKGROUND OF THE DISCLOSURE

Magnetic materials can be made to have preferred magnetic orientationinduced by applying an external magnetic field during deposition. Thedeposition method includes but not limited to electrodeposition orphysical vapor deposition. Obtaining a uniform and large enough fieldacross large dimensions, such as 200 mm or 300 mm wafers, is one of themajor challenges associated with building magnetic devices on 200 mm or300 mm wafers. The shape anisotropy of a small patterned area demandsadditional field strength requirement in additional to the fieldrequirement of a blanket symmetric film due to the demagnetizationeffect. By depositing a blanket film, or a film close to blanketcontinuity, the preferred magnetic orientation can be induced with asmaller magnetic field, which is more attainable and much lessexpensive.

U.S. Pat. No. 3,853,715 (“Elimination of Undercut In Anodically ActiveMetal During Chemical Etching”) describes a frame plating methodology toachieve magnetic orientation in a patterned structure. The methodemployed includes depositing a blanket seed layer, putting on frameresist for patterning, plating up the structure, block resist patterningto protect the structure, chemically etching away the rest, andstripping the resist. However, a drawback with this approach is the seedlayer under the thin frame serves as a path for undercut during chemicaletching of the remaining materials. The consequence of the undercuteasily destroys the whole pattern by lifting the resist frame and etchedaway the wanted structure. The undercut also restricts the minimumdimension that can be built in this approach to be millimeters.

Accordingly, the present invention relates to an improved method, whichincludes double etching for manufacturing a device pattern, eliminatesundercut issue, provides a reliable process to build devices rangingfrom nanometer size to tens of centimeters size range

SUMMARY OF THE DISCLOSURE

In accordance with the invention, the method includes in a series ofsteps patterns a magnetic structure by putting down a layer ofdielectric as the substrate (step 1), depositing a thin adhesion layerand a thin seed layer (step 2), putting thin resist frame to pattern thestructure (step 3), depositing up the structure and the field area (step4), stripping the resist frame (step 5), etching the seed layer and theadhesion layer exposed below the resist frame down to the dielectricsurface by sputter etch or reactive ion etch (step 6), etching the fieldmagnetic materials by electrolytic etching where the device structuresare typically isolated from the field (step 7), and etching the seedlayer and adhesion layer in the field by sputter etch, and/or reactiveion etch (step 8).

Specifically, an aspect of the method of patterning magnetic devices andsensors by double etching includes:

-   -   forming a layer of dielectric on a substrate;    -   depositing a thin adhesion layer and a thin seed;    -   applying a thin resist frame to pattern a structure;    -   cleaning the metal surface to prepare for plating;    -   electroplating to fill up the structure and the uncovered area,        which uses a paddle cell with a permanent magnet providing        magnetic field to induce magnetic orientation stripping the        resist frame;    -   etching the seed layer/adhesion layer exposed below the resist        frame down to the dielectric surface by either reactive ion etch        and/or physical sputtering etch;    -   etching the rest of magnetic materials and the seed layer by        electrolytic etching when the field is typically electrically        isolated from the device structure.    -   and etching the remaining adhesion layer in the field.

The above steps are repeated for building structures with multiplelayers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the disclosed process flow of the present disclosure.

FIG. 2 illustrates the patterning results from a prior art method.

FIG. 3 illustrates examples of structures that can be made with thedisclosed methodology together with a planar view of a typicalelectrical isolated device structure.

DETAILED DESCRIPTION OF THE DISCLOSURE

A more complete appreciation of the disclosure and many of the attendantadvantages will be readily obtained, as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 illustrates a double etch patterning process flow. Thismethodology completely eliminates undercut issue and provides a reliableprocess to build devices ranging from nanometer size to tens ofcentimeters size range. Etching steps 6 and 8 can be chemical etching ordry etching processes, including but not limited to plasma etch, sputteretch, reactive ion etch, and chemical etch.

Etching step 7 uses electrolytic etching, which uses electrical currentto dissolve the unwanted film in a sodium chloride solution, which doesnot attack the desired device structure due to electrical isolation ofthe device structure and the unwanted magnetic film in the field.

This invention discloses a few major improvements over the existingmethodology. More specifically, it patterns a magnetic structure by:

-   -   1. Forming a layer of dielectric on the substrate, which        includes silicon oxide, silicon oxynitride, low-k dielectric,        and a polymer such as a polyimide, or resist;    -   2. Depositing an adhesion layer and a seed layer, which may        include Ta, TaN, Ti, TiN, Cr, or the combinations thereof as the        adhesion layer and a thin layer of metallic film from various        deposition techniques, such as Ni, Fe, Co, Cu, and alloys        thereof;    -   3. Applying a thin resist frame to pattern the structure;    -   4. Cleaning of metal surface to prepare for plating;    -   5. Electroplating to fill up the structure and the uncovered        field area, which uses a paddle cell with a permanent magnet        providing magnetic field to induce preferred magnetic        orientation;    -   6. Stripping the resist;    -   7. Etching the seed layer/adhesion layer exposed below the        resist frame down to the dielectric surface by sputtering etch        and/or reactive ion etch;    -   8. Etching the remainder of magnetic materials and the seed        layer, in which electrochemical etching is used since the        typical device features are well isolated from the field; and    -   9. Etching the adhesion layer either by sputtering or reactive        ion etch.

The above steps are repeated for building structures with multiplelayers.

In a preferred embodiment, suitable substrates may include but they arenot limited to: silicon, quartz, glass, sapphire, metal, galliumnitride, gallium arsenide, germanium, silicon-germanium,indium-tin-oxide, alumina (Al₂O₃), and plastic. The substrate may berigid or flexible.

In another preferred embodiment, the dielectric layer may be siliconoxide, silicon oxynitride, low-k dielectric, and a polymer such as apolyimide, or resist

In another preferred embodiment, the thin adhesion layer may include butit is not limited to Ta, TaN, Ti, TiN, Cr, and combinations of thereof.

In another preferred embodiment the seed layer may include but is notlimited to Ni, Co, Fe, Cu, Ru, Rh, Zn, Ag, Au and the alloys thereof.The seed layer is typically deposited to a thickness from about 5 nm toabout 500 nm. The layer may be deposited by PVD, CVD, ALD or byelectroless deposition techniques

In another preferred embodiment, the electroplating can be carried outusing an anode such as Pt, Ti or other soluble metals such as Ni, Co,Fe, Cu and the alloys thereof, and a cathode, which is the wafersubstrate to be plated with a conductive seed layer.

In another preferred embodiment, the electroplating is generally carriedout employing a current density of about 1 to about 100 milliamps/cm²,more typically about 1 to about 50 milliamp/cm² and even more typicallyabout 5 to about 20 milliamps/cm². Also, the electroplating is generallycarried out at temperatures of about 10° C. to about 80° C.

The general dimensions for electroplating are between about 10 nm andabout 10 cm. The aspect ratio is from about 0.5 to about 10.

In another preferred embodiment, the etching of adhesion layer and seedlayer may include conventional dry etching for example, sputtering,reactive ion etching, ion beam etching and/or plasma etching.

The electrolytic etching utilizes an electrical current to dissolve theelectrically connected metal film, with the metal film being the anode,and a counter electrode of Pt, Ti, Cu, Ni, steel, or other conductivematerials being the cathode. A typical electrolytic etch solution issodium chloride with pH range of −1 to 3. The etching solution providessufficient conductivity, and can be made to be aggressive toward thespecific metal dissolution. Any other desired chemical may be used forthe etching treatment.

Obviously, numerous modifications and variations of the disclosure arepossible in light of the above disclosure. It is therefore understoodthat within the scope of the appended claims, the disclosure may bepracticed otherwise than as specifically described herein.

1. A method of patterning magnetic devices and sensors by doubleetching, which comprises: forming a layer of dielectric on a substrate;depositing a thin seed layer or a combination of adhesion layer and seedlayer; applying a thin resist frame to pattern a structure; cleaning themetal surface to prepare for plating; electroplating to fill up thestructure and the uncovered field area, which uses a paddle cell with apermanent magnet providing magnetic field to induce magnetic orientationstripping the resist frame; etching the seed layer/adhesion layerexposed below the resist frame down to the dielectric surface; etchingthe rest of magnetic materials and the seed layer by electrolytic etch.;and etching the adhesion layer in the field.
 2. The method of claim 1,above steps are repeated for a multiple level build.
 3. The methodaccording to claim 1, wherein the substrate is selected from the groupconsisting of silicon, quartz, glass, sapphire, metal, gallium nitride,gallium arsenide, germanium, silicon-germanium, indium-tin-oxide,alumina, and plastic.
 4. The method according to claim 1, wherein thedielectric layer is selected from the group consisting of silicon oxide,silicon oxynitride, low-k dielectric, and a polymer such as a polyimide,or resist;
 5. The method according to claim 1, wherein the thin adhesionlayer is selected from the group consisting of Ta, TaN, Ti, TiN, Cr,combinations thereof.
 6. The method according to claim 1, wherein thethin seed layer is selected from Ni, Fe, Co, Cu, Ru, Rh, Ag, Ag, Zn, andthe alloys thereof.
 7. The method according to claim 1, wherein the thinseed layer/adhesion layer has a thickness from about 5 nm to about 500nm.
 8. The method according to claim 1, wherein the thin seedlayer/adhesion layer is deposited by PVD, CVD, or by electrolesstechniques.
 9. The method according to claim 1, wherein the cleaningbefore electrodeposition can be ashing in reducing gas, such as forminggas, ammonia, or hydrogen, or chemical cleaning, such as acid rinse, orphysical clean, such as sputtering etch.
 10. The method according toclaim 1, wherein the electroplating is carried out employing a currentdensity of about 1 to about 100 milliamps/cm².
 11. The method accordingto claim 1, wherein the electroplating is carried out at temperatures ofabout 10° C. to about 80° C.
 12. The method according to claim 1,wherein the electroplating is carried out employing a current waveformof about 5 to about 20 milliamps/cm².
 13. The method according to claim1, wherein the electroplating is carried out by a paddle cell with amagnetic field applied during the deposition.
 14. The method accordingto claim 1, wherein the seed layer/adhesion layer etching is carried outby dry etching, sputtering etch, reactive-ion etching (RIE),wet-chemical etching, or ion-beam etching.
 15. The method according toclaim 1, wherein the electrolytic etching uses externalcurrent/potential supply to dissolve the metal film in contact with thepower, with the metal film being electrically connected to the anode (orpositive potential), and a counter electrode connected to the cathode.The solution can be sodium chloride with pH range between −1 to 3 or anyother desired chemicals specific to the metal to be etched.
 16. Themethod according to claim 1, wherein the electrolytic etching uses acurrent density range between 10 milliamps to 10 amps.